1. Field of the Invention
Example embodiments of the present invention relates to methods of fabricating a semiconductor device. Other example embodiments relate to methods of forming a finer pattern of a semiconductor device using a double patterning technique.
2. Description of the Related Art
Miniaturization of a pattern in semiconductor fabrication may be necessary for higher integration of a semiconductor device. In order to integrate more elements in a narrower area, the size of a discrete element may be reduced. Pitch, which is the sum of a width and a distance of a desired pattern, may be reduced. With a design rule of a device decreasing resolution of a photolithography process, which may be used to form the pattern of a semiconductor device capable of meeting certain requirements, may be limited. Example requirements may include a desired line and space pattern (hereinafter referred to as “L/S pattern”). The formation of a pattern having a finer pitch may also be limited.
Various pattern formation techniques have been proposed in order to overcome the resolution limitation of the photolithography process. Conventional methods include a pattern formation technique using two sheets of photomasks. FIGS. 1A through 1G are sectional views illustrating a conventional method of forming a finer pattern of a semiconductor device using two sheets of photomasks.
Referring to FIG. 1A, a material layer 12 to be etched, a first mask material layer 14, a second mask material layer 16 and/or a first photoresist layer 18 may be sequentially formed on a substrate 10. A light beam 11 may be irradiated on the first photoresist layer 18 through a first exposure mask 20 formed of a first transparent substrate 22 having a first light shield layer pattern 24.
Referring to FIG. 1B, the first photoresist layer 18 may be developed to form a first photoresist pattern 18A. Using the first photoresist pattern 18A as an etch mask, the second mask material layer 16 may be etched so as to form a second mask material layer pattern 16A.
Referring to FIG. 1C, a second photoresist layer 26 may be formed on the resultant structure having the first photoresist pattern 18A and the second mask material layer pattern 16A. A light beam 11 may be irradiated on the second photoresist layer 26 through a second exposure mask 30 formed of a second transparent substrate 32 having a second light shield layer pattern 34. The second light shield layer pattern 34 of the second exposure mask 30 may be formed not to overlap the first light shield pattern 24 of the first exposure mask 20 and/or may be disposed in the middle portion between the first light shield pattern 24.
Referring to FIG. 1D, the second photoresist layer 26 may be developed to form a second photoresist pattern 26A. Using the second photoresist pattern 26A and the second mask material layer pattern 16A as etch masks, the first mask material layer 14 may be etched to form a first mask material layer pattern 14A.
Referring to FIG. 1E, the material layer 12 may be anisotropically etched using the first mask material layer pattern 14A, the second mask material layer pattern 16A and/or the second photoresist pattern 26A as etch masks to form a material layer pattern 12A. The second mask material layer pattern 16A may be removed concurrently with the etching. A remnant layer 26B of the second photoresist pattern 26A may remain on the first mask material layer pattern 14A.
Referring to FIG. 1G, the first mask material layer pattern 14A and/or the remnant layer 26B, which may remain on the material layer pattern 12A, may be removed.
The conventional method of forming a pattern as described above is limited in the formation of a finer pattern of about 40 nm or less. The second photoresist pattern 26A may be formed between the second mask material layer pattern 16A in the conventional pattern formation method. When the distance between the second mask material layer pattern 16A and the second photoresist pattern 26A is narrow, a bridge may form between the second mask material layer pattern 16A and the second photoresist pattern 26A during the formation of the second photoresist pattern 26A. Developer solution may not sufficiently penetrate into a bottom portion during the formation of the second photoresist pattern 26A because the distance between the second mask material layer pattern 16A and the second photoresist pattern 26A becomes narrower. Further, it may be necessary to control critical dimension (CD) uniformity in the fabrication of a finer pattern of 40 nm or less. It may be necessary to employ a separate organic anti-reflective coating (ARC) layer during the formation of the second photoresist pattern 26A in the conventional double patterning technology as described above in order to increase CD uniformity. However, bridges may form if the organic ARC inside a narrow space between the second mask material layer pattern 16A and the second photoresist pattern 26A is not sufficiently removed.
When coating the resultant structure having the second mask material layer pattern 16A with a photoresist material in order to form the second photoresist pattern 26A, the photoresist material may not uniformly spread due to remnant materials such as a bridge existing between the second mask material layer pattern 16A. It may be difficult to control pattern fidelity during the fabrication of a finer pattern.
FIG. 2 is a photograph illustrating a photoresist material after coating in the conventional method of forming a finer pattern. FIG. 2 is a photograph illustrating the formation of a section of the second mask material layer pattern 16A. The second mask material layer pattern 16A may be coated with a photoresist material for the formation of the second photoresist pattern 26A.
As shown in FIG. 2, the coated photoresist material may not uniformly spread due to remnant materials between the second mask material layer pattern 16A.
In the double patterning process, it may be desirous to control the formation of defects. The hard mask may remain on the substrate after the first patterning process. For example, the first mask material layer 14 in FIG. 1B may be partially damaged during the etch process causing a pitting phenomenon. The layers under the first mask layer 14 may be removed through the broken hard mask to generate an empty space.
FIGS. 3A and 3B are photographs illustrating that a pitting phenomenon is generated in the conventional method of forming a finer pattern; and FIG. 4 is a photograph illustrating a protrusion phenomenon caused by pitting in the conventional method of forming a finer pattern.
FIGS. 3A and 3B are photographs of an upper surface and a section of a substrate illustrating a pitting phenomenon which may occur on the substrate after the first patterning process is performed.
As a bottom photoresist layer is formed on a substrate by coating under conditions favorable for the generation of the pitting phenomenon, as shown in FIGS. 3A and 3B, and then baked by a bake process, a protrusion phenomenon may occur as shown in FIG. 4. If a photoresist pattern is formed thereon, defocusing and/or a pattern bridge phenomenon may occur.
The conventional art acknowledges a technique of patterning an etched layer using a spacer pattern, formed by a spacer having a smaller size, as a hard mask. However, when using a spacer pattern as a hard mask, a pair of spacers disposed to the right and/or left of a central pattern may not have a uniform thickness. Spacers may be formed to have a larger thickness than a desired thickness in order to make the thickness of the right and/or left spacers more uniform. After the spacers are used as a hard mask, the spacers may not be sufficiently removed. Further, the hard mask having the spacer shape may be shaped to surround the pattern disposed at the center. Therefore, in the case of fabricating a line pattern using the spacer, a separate trimming process may be necessary to separate the spacer into a discrete line pattern.